Rent-a-miner attacks seems to be another amusing example of when the existence of a market can break the system.

For example, voting works well in a democracy, but if we can sell votes, democracy would likely collapse because rich organizations would buy it up and control all politics. (Some say this is already true; but you know it would be way worse if votes were openly sellable).

Satoshi foresaw people trying to mount a 51% attack by buying a ton of machines, and so he went to great lengths to ensure this was unlikely using mining. I don't think Satoshi foresaw the liquid AWS-like market for instant hashing power. The ability to mount a limited-time 51% attack makes the attack literally 1000x easier than a buy-machine 51% attack.